The purpose of this experiment is to identify the extrahypothalamic central neural substrates underlying hyperphagia and obesity. Preliminary work indicated that electrolytic lesions anterior and lateral to the ventromedial hypothalamic nucleus which produced hyperphagia and obesity, also resulted in terminal degeneration in the central gray and in the supramamillary region. Lesions in these regions should also produce hyperphagia and obesity, and permit further tracing of the descending pathways involved in the regulation of feeding. In this study behavioral and anatomical procedures will be used to: (1) verify that lesions of the central gray and supramamillary region do produce hyperphagia and obesity, and (2) trace the pattern of descending terminal degeneration resulting from these lesions. DC lesions will be made in each of the regions where terminal degeneration was observed previously. Some of the animals in each group will be lesioned bilaterally and both the dynamic and static phases of hyperphagia will be followed. Other animals will receive unilateral lesions and their brains will be prepared for microscopic examination with the Pope-Giolli modification of the Fink-Heimer silver stain for degenerating axons and terminals. With these methods the descending pathways involved in hyperphagia can be traced beyond the midbrain level. Identification of the neural substrates underlying feeding will add to our understanding of the neural organization of behavioral phenomena and enable further investigations of the mechanisms of action of these structures.